Silicate clay.(Morshed)

Silicate clay are the electro-microscopic clay minerals, which diameter less than 2 microns.

1. Silicate Clay Made By Group No: 03

2. Course Code: AG-3103 Course Title: Soil Physics and Chemistry Roll No: ASH1514009M ASH1514020M ASH1514026M ASH1514027M ASH1514028M ASH1514O37M ASH1514046M ASH1514047M ASH1514054M ASH1514058M ASH1414070M

3. Contents: Definition of Silicate Clay Some Important Features of Silicate Clays Basic Structure of Silicate Clays Classification of Silicate Clays Characteristics of Kaolinite minerals Characteristics of Mica minerals Characteristics of Vermiculite minerals Characteristics of Smectite minerals Characteristics of Chlorite minerals Characteristics of Interstartified minerals References

4. Definition of Silicate Clay: Silicate clay are the electro-microscopic clay minerals, which diameter less than 2 microns. It is the textural classes of soil and developed more in the horizontal axis than the vertical axis of soil profile. It is the characteristics minerals of the earths near surface environments. They form in soils and sediments. E.g : kaolinite, Micas, Vermiculite, Chlorite etc.

5. Some Important Features of Silicate Clays: Chemical Composition: The chemical analysis of clay indicates the presence of silica, alumina, iron and combined water. These make up from 90-98 percent of the colloidal clay. The soil colloidal matter contains plant nutrients like Ca , Mg and K etc . Shape : Silicate clay minerals have been examined by electron microscope and found that the particles are laminated made up of layers of plates or flakes or even rods. Each clay particle is made up of a large number of plates like structural units.

6. Some Important Features of Silicate Clays: Surface Area: The surface area of a clay particle is usually defined as the area of the particle that is accessible to ions or molecules when the clay is in an aqueous solution. All clay particles (finer fraction of soil) must expose a large amount of external surface. Surface areas of clay particles can be measured by using cetylpyridinium bromide (dissolving in water) for fully dispersed clay suspension. Surface area for clays like vermiculites and some mixed layer clays 300-500 m 2 /g; micaceous clays 100-300 m 2 /g ; kaolinitic clays 5-100 m 2 /g; and a morphous clays have surface areas between 100 and 500 m 2 /g.

7. Some Important Features of Silicate Clays: Electronegative Charge: Clay micelles (micro cells) carry negative charges and so a number of oppositely charged ions ( cations ) are attracted to each colloidal clay crystal. The colloidal clay particles have inner ionic layer (surfaces of highly negative charge) and the outer ionic layer (highly positive charge layer). Adsorbed Cations : Clay micelles adsorb a number of cations -humid, arid and semiarid regions colloids- cations are H + , Al 3+ , Ca 2+ , Mg /+ , Na +  and K + . Cations adsorbed on the clay colloids very oftenly determines the physical and chemical properties of the soil and thereby influence the plant growth.

8. Basic Structure of Silicate Clays: Two structural units are involved in most of the silicate clay minerals. They are Tetrahedral silica sheets (Silica tetrahedral units) Octahedral alumina sheets (Alumina octahedral units) The tetrahedral silica sheets are attached to the octahedral alumina sheet in the structure.

9. Tetrahedral Silica Sheet: The main structural unit of silicates is a tetrahedral cluster containing one silicon atom and four oxygen atoms. Three oxygen in the sheet and one in the above. The size of [ SiO 4 ] 4- tetrahedral is relatively stable, with Si-O bond length varying from 0.161 to 0.164 nm, O-to-O distance about 0.264 nm .

10. Octahedral Alumina Sheet: The alumina consists of two sheets of closely packed oxygen atoms or hydroxyl groups which are held together by alumina atoms in such a way that one alumina is surrounded by six oxygen atoms or hydroxyl group. The normal O-to-O distance is 2.60A and the common OH-to-OH distance is about 3A .The thickness of the unit is 5.05A in the clay mineral structure.  

11. Classification of Silicate Clays: Amorphous, e.g : Allophane group Crystalline 2 layer type(1:1 type) Equidimensional (kaolin group), e.g : Kaolinite, Nacrite , Dickite , Anauxite Elongate ( halloysite group), e.g : Endellite , Metahalloysite 3 layer type(2:1 type) Expending lattice type Equidimentional Smectite groups: e.g : Montmorillonite , Bidellite , Sauconite Vermiculite groups: e.g : Vermiculite Elongate, e.g : Nontronite, Saponite , Hectorite

12. Classification of Silicate Clays: Non-expending lattice type Muscovite Biotite Phlogopite Mixed layer type Chlorite group Chain structure type Attapulgite Sepiolite Polygorskite

13. Characteristics of Kaolinite minerals: Name of Origin: Named after the locality. Color: White, Brownish white, Grayish white, Yellowish white, Grayish green . Locality: Kao-Ling, China, Germany, India, Australia, Malaysia, Brazil etc. Found in moist, warm to hot, sub-humid and humid soils , acidic . Chemical Formula : Al 2 Si 2 O 5 (OH) 4 Composition: Molecular Weight = 258.16 gm(Al=20.90 %, Si=21.76 %, H=1.56 %, O=55.78 %)

14. Characteristics of Kaolinite minerals: Surface area is kaolinite ranged from 5-20 m 2 /g. It is one of the most wide s pread clay minerals in soils. It is most abundant in soils of warm moist climates and is a prominent constituent of oceanic sediments. CEC usually vary from 3-15 meq ( milliequivalent )/100g.

15. Characteristics of Mica minerals: Mica is a mineral name given to a group of minerals. Of the 37 known species of the mica group(Muscovite, Paragonite , lepidolite , biotite etc.) They are all silicate minerals, known as sheet silicates because they form in 2 silica sheets with a central alumina sheet. Chemical Formula: The general formula for minerals of the mica group is XY 2–3 Z 4 O 10 (OH , F) 2 with X = K, Na, Ba, Ca , Cs, (H 3 O), (NH 4 ); Y = Al, Mg, Fe 2+ , Li, Cr, Mn , V, Zn; and Z = Si, Al, Fe 3+ ,Be , Ti. Example: Lepidolite K( Li,Al ) 3 (AlSi 3 O 10 ) (O,OH, F) 2 ;Biotite K(Mg, Fe) 3 (AlSi 3 O 10 ) ( OH) 2 ; Muscovite KAl 2 (AlSi 3 O 10 )( OH) 2

16. Characteristics of Mica minerals: Color: Purple, rosy , silver, dark green, brown , black; yellowish-brown, green white; colorless. Specific gravity: 2.8-3.1 and Melting point: 700-1000 C Jharkhand state in India had the largest deposits of mica in the world, China, US, South Korea Canada, Europe etc are found. Micas are fairly light and relatively soft . The sheets are flexible. It is heat-resistant and does not conduct electricity . CEC ranges from 15-40 meq /100kg. External surface area 70-100 m 2 /g and internal area 1.0 nm  

17. Characteristics of Vermiculite minerals: Vermiculite is a hydrated magnesium aluminum silicate mineral. Found in Australia, Brazil, Bulgaria, Kenya, Russia, South Africa, Uganda, USA and Zimbabwe. Chemical Formula: (Mg, Fe ++ ,Al) 3 ( Al,Si ) 4 O 10 (OH) 2 •4(H 2 O) Composition: Molecular Weight = 504.19 gm (Mg=8.68 %, Al=23.01 %, Fe=9.97 %, Si=5.57 %,H=2.00 %, O=50.77%) Specific gravity: 2.4-2.7

18. Characteristics of Vermiculite minerals: Color: Colorless, Green, Gray white, Yellow brown . CEC ranges from 100-180 meq /100kg . External surface area 500-600 m 2 /g and internal area 1-1.5 m 2 /g. Shape of the vermiculites are platy, flakes.

19. Characteristics of Smectite minerals: Members of the smectite minerals can be divided into 2 groups. The dioctahedral minerals ( montmorillonite , beidellite , and Nontronite) and the trioctahedral minerals ( hectorite , saponite , and sauconite . Size: Naturally occurring smectite ranges in size from 0.25 microns up to 0.75 microns. Shape: Irregular flakes.

20. Characteristics of Smectite minerals: They are characterized by alumina octahedral layer sandwiched between two silica tetrahedral layers. CEC ranges varies from 80-150 meq /100g soil. Specific surface area ranges from 700-800 m 2 /g

21. Characteristics of Chlorite minerals: Chlorites are basically iron-manganese silicates with some aluminum present. Members of the chlorites minerals are Clinochlore , Nimite , Ripidolite , Odinite etc. Chemical Formula: ( Mg,Fe ) 3 ( Si,Al ) 4 O 10 (OH) 2 ·( Mg,Fe ) 3 (OH) 6 Color: Various shades of green; rarely yellow, red, or white .

22. Characteristics of Chlorite minerals: Chlorite is commonly found in igneous rocks, sedimentary rocks and metamorphic . Specific gravity: 2.6-3.3 Chlorite is so soft that it can be scratched by a finger nail.

23. Characteristics of Interstartified minerals: Many clay materials are mixtures of more than one clay mineral. Such minerals are called as mixed layer or interstratified minerals. E.g : Chlorite-vermiculite, Mica- Smectite . As the mixing ratio for the two component layers varies. References: https:// en.wikipedia.org/wiki White R.E., 1987. Introduction to the Principles and Practice of Soil Science.

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